autochthonal vs autochthonous

autochthonal and autochthonous both are adjectives.

Word	Noun	Adjective	Verb	Adverb
autochthonal	No	Yes	No	No
autochthonous	No	Yes	No	No

As adjectives, autochthonal and autochthonous are synonyms defined as:

Other synonyms of autochthonal include autochthonic, endemic, indigenous.

autochthonal (adjective)	autochthonous (adjective)
originating where it is found	of rocks, deposits, etc.; found where they and their constituents were formed
	originating where it is found